Study On Mixing Mechanism And Simulation Of Laser Cladding Alloy Powder

Functionally graded material is a type of material in which the composition and structure of the material change continuously from any direction of the material so that the properties and functions of the material also change in gradient.Functionally graded materials,as a new type of materials,have become the focus of research in the field of materials due to their excellent structure and properties.However,there are few studies on powder mixing in the preparation of functionally gradient materials and the relevant theories have not been perfected.Therefore,based on the relevant mechanism of powder mixing and the theory of gas-solid two-phase flow,this paper makes an in-depth study on the pre-treatment powder mixing process of preparing functionally gradient materials.The specific content is as follows:(1)Based on the relevant theoretical knowledge of gas-solid two-phase flow and aiming at the actual working conditions of protecting nitrogen and alloy powder two-phase flow,the flow type was determined to be turbulence through the calculation of Reynolds number.Reynolds time-average method was used for numerical simulation,and the navier-stokes equation after Reynolds time-average method was selected for the gas phase control equation,and the standard two-equation turbulence model was selected for the calculation process.When the volume fraction of solid particles was less than 10%,DPM model was used.(2)Fluent finite element analysis method was used to simulate the powder flow field.When the powder concentration and particle entry velocity were different,the variation rule and influence of changing powder parameters on the fluid velocity field were investigated.In the case of different baffle layers,baffle mesh shape,baffle installation distance and cylinder length,the variation rule and influence of changing the internal structure of the mixer on the powder velocity flow field were investigated.(3)Based on the calculation and detection method of powder mixing evenness,grouping single factor experiment was carried out to verify the rationality of mixing process parameters.The single factor experiment was carried out with the self-designed and built mixing equipment.The experiment is divided into two parts.One is to explore the influence of powder mixing uniformity in different proportions with and without mixing powder.Second is to explore the influence of the number of baffle layers,the shape of baffle mesh,baffle installation position and the length of powder mixer on the uniformity of powder mixing.The surface scanning function of scanning electron microscope was used to obtain the distribution maps of Fe and Ni elements under different conditions,and the number of 316L and IN718 particles under different conditions was obtained by image ej after image processing,and the corresponding powder mixing uniformity was calculated.(4)In the case of different baffle layers,baffle screen shape,baffle mounting distance and cylinder length,the velocity value in the direction of the mixer axis was output through Fluent post-processing,and the fitting curve was obtained by data fitting between the mean velocity value and the uniformity value calculated by experiment.The correlation between velocity and uniformity and the mechanism of fast mixing of alloy powder driven by air load were investigated.